Apparatus for measuring in a continuous manner the oxygen in a molten metal

ABSTRACT

Apparatus for the continuous measurement of oxygen contained in a molten metal which comprises A. A SOLID OXYGEN ELECTROLYTE TUBE; B. A REFERENCE ELECTRODE HAVING KNOWN OXYGEN POTENTIAL IN CONTACT WITH THE INNER SURFACE OF THE TUBE; C. MEANS FOR MEASURING THE ELECTROCHEMICAL POTENTIAL PRESENT BETWEEN THE INNER AND OUTER SURFACES OF THE TUBE; AND D. INSULATING MEANS TO PROTECT THE SOLID OXYGEN ELECTROLYTE TUBE AGAINST CHEMICAL ATTACKS, THERMAL SHOCKS AND MECHANICAL STRESS DUE TO THE CONTACT WITH THE LIQUID MOLTEN METAL. The insulating means is a tube made of a metal containing substance having a high resistance to mechanical stress, to thermal shocks, to chemical attack, to splashing of the metal which is to be tested and to the slag of the metal which is to be tested. In addition the insulating means closely surrounds the solid oxygen electrolyte tube and is open at the bottom so that the outer surface of the tube can be directly contacted with the molten metal which is to be tested.

United States Patent Richardson [541 APPARATUS FOR MEASURING IN A CONTINUOUS MANNER THE OXYGEN IN A MOLTEN METAL [72] Inventor: Frederick Denys Richardson, Epsom, Surrey. England [73] Assignees: Metallurgie Hoboken, Brussels, Belgium;

RST International Metals Limited, London, England, part interest to each l22| Filed. Jan. 27, I969 ]?l Appl. Nu 794,335

[ 1 May 9,1972

OTHER PUBLICATIONS G. R. Fitterer, Journal of Metals. Reprint pp. 1- 6, August [966 Primary Examiner-G. L. Kaplan Attorney-Fred C. Philpitt 5 7] ABSTRACT Apparatus for the continuous measurement of oxygen contained in a molten metal which comprises a. a solid oxygen electrolyte tube;

b. a reference electrode having known oxygen potential in contact with the inner surface ofthe tube;

c. means for measuring the electrochemical potential present between the inner and outer sutfaces ofthe tube; and

d. insulating means to protect the solid oxygen electrolyte tube against chemical attacks. thermal shocks and mechanical stress due to the contact with the liquid molten metal.

The insulating means is a tube made ofa metal containing substance having a high resistance to mechanical stress. to thermal shocks, to chemical attack, to splashing ofthe metal which is to be tested and to the slag of the metal which is to be tested. in addition the insulating means closely surrounds the solid oxygen electrolyte tube and is open at the bottom so that the outer surface of the tube can be directly contacted with the molten metal which is to be tested.

16 Claims, 3 Drawing Figures wimigm 919v TLSSLMF) sum 3 m 3 APPARATUS FOR MEASURING IN A CONTINUOUS MANNER THE OXYGEN IN A MOLTEN METAL This invention relates to a process and to an apparatus permitting to measure in a continuous manner by an electrochemical process the amount of oxygen contained in a molten metal, more particularly in copper, lead or their alloys. The invention is for example useful for all processes of metal manufacture where the percentage of oxygen in the metal produced is critical.

The present invention relates more particularly to an immersion device which serves to detect in an electromechanical manner the oxygen potential in the molten metal, and to means for measuring and converting the said potential into ox ygen percentage.

The classical methods of chemical analysis of metal materials, often from samples which take a long time to prepare, have in recent years been less and less used, and more rapid methods have been employed giving rapidly the reading of the measurement, from the bath of molten metal.

Methods are known for analysing the oxygen contained in liquid metals, more particularly in liquid copper, which are based upon measurement of the electromotive force developed between the two faces of a solid electrolyte when one face is in contact with the liquid being tested and other with a system in which the oxygen potential is controlled at a constant value. It is possible to use as the solid electrolyte ceramic bodies resistant to high temperatures and having a good ionic conductivity, such as zirconia (ZrO,) which has been stabilized or partially stabilised with CaO, no, or MgO.

One face of the said solid electrolyte is in contact with the metal, for instance with liquid copper containing oxygen in solution, the concentration of which is to be measured and in which a collector of current made of refractory metal is immersed. The other face is placed in contact with a reference electrode working with a known oxygen pressure, for instance with the known mixture Ni-NiO or with an appropriate gas mixture, and connected with another collector of current formed for instance ofa platinum wire.

The measurement of the voltage E between the said two current collectors makes it possible to establish the percentage of O in the liquid metal of the formula:

g In, p (liquid metal) in which R the gas constant T= the absolute temperature it the valency of the oxygen ion, equal to 2 F= the value ofa Faraday p the partial oxygen pressure and the known relationship between oxygen pressure and concentration for the metal concerned.

The said voltage is measured by an electrometer the impedance of which is sufficiently high, relative to that of the measuring cell.

The present invention consists in a process and apparatus for the measurement in a continuous manner of the oxygen contained in a molten metal such as copper or lead, for detect ing in an electrochemical manner the oxygen potential of the molten metal, comprising means for measuring the electrical potential developed between the two faces of a solid electrolyte which are placed in contact with phases the partial oxygen pressures of which are different from each other, characterized by the use of a tube of high resistance to mechanical and thermal shock, to chemical attack, to splashing by the metal being treated, and to attack by the slag on the metal being treated, which tube surrounds the solid electrolyte and forms a contact electrode with the molten metal,

According to another characteristic feature of the present invention, a block of copper or other metal substance which is of low melting point, may be arranged below and/or around the solid electrolyte in such a manner that the metal block shall be placed in contact with the bath and shall absorb heat by melting, whilst permitting a progressive heating of the electrolyte.

As appropriate substances for chemical and mechanical protection, metals or refractory alloys or cermets may be cited, for instance ferritic steel, iron, kanthal or the cermet Cr Ano,

Use may be made of a reference electrode consisting of a current of air of constant flow, which is continuously renewed to ensure a constant value of the content of oxygen.

Generally, it is undesirable that air shall pass in an amount such that there shall be an inner cooling of the reference electrode, as this could act unfavorably upon the electromotive force.

According to a characteristic feature of the present invention, the various elements of the apparatus are arranged co-axially in a particularly simple and compact manner as one strong unit, easy to handle.

The invention is described hereinafter with reference to the accompanying drawings which show diagrammatically and by way of example one mode of carrying the invention into effeet.

In the drawings,

FIG. 1 is a view showing the structure of the clipping or immersion apparatus.

FIG. 2 is a view showing another mode of construction of the clipping or immersion apparatus.

FIG. 3 is a view showing the dipping or immersion apparatus adapted to a casting ladle for copper.

Referring to FIG. 1 an elongated cup or tube 2 closed at one end, made from the solid electrolyte is fixed by means of a refractory cement 4 to a sheath 3 made of a refractory material (metal, alloy, cermet)which is conducting of electrical current and is highly resistant to chemical and mechanical actions. The end of the tube 2 is placed in contact with a molten bath 1, the contents of oxygen of which are to be measured. The sheath 3 forms one of the current conductors serving for the electrical measurements. This allows of instantaneously making said electrical measurements and of obtaining a compact and strong unit device, easy to handle. The sheath 3 may, for those parts which are not exposed to chemical actions, be prolonged by a portion 17 made of ordinary stainless steelv An injection conduit 5 made of refractory material and nonconductor of current, for instance of aluminous refractory material, extends inside the sheath 3 as near to the bottom of the electrolyte tube as possible, to sweep air at the point of the electrical contact with the bottom of the tube 2 as shown by the arrows 15 in the drawing.

A current collecting wire 6 connected with the sheath 3 on the one hand, and a current conductive wire 7, such as for example a wire of platinum or platinum-rhodium, in contact with the bottom of the tube 2 on the other hand, are connected with a sensitive electrometer (not illustrated).

When slag is absent from the metal under test the end of the sheath 3 may advantageously be shaped so as to have a tongue which extends 4 to 5 centimeters beyond the solid electrolyte 2, so as to reduce thermal shock when immersed. For this purpose the tip can be dipped into the metal and held there for some time prior to immersing the electrolyte.

Referring now to FIG. 2 of the drawings, the tube 2, the sheath 3, the cement 4, are made as shown in FIG. 1. A block of copper 8 may be placed below the solid electrolyte 2 in contact with the molten metal bath 1 to reduce the effect of ther mal shocks upon the electrolyte 2 which is fragile and protect the electrolyte from slag when immersed. The said block is fixed to the sheath 3 by means of a screw 19, made for instance of steel. A longitudinal channel 18 is advantageously bored in the block of copper 8, permitting the escape of the gases held between the capsule and the block of copper.

At the upper part of H0. 2, a modification of the invention has been shown: cooling fluid passes through a device 10 for cooling the head of the apparatus in the direction of the arrows 16 for protecting the head of the apparatus against the effects of flames or of a high thermal radiation.

in order to improve the contact between the solid electrolyte 2, the reference electrode, and the current collector, it may be useful to place on the bottom of the tube 2 silver filings or a small silver lead 11 (FIG. 2) which can melt when the immersion apparatus is introduced into the bath of liquid metal The current collector may be formed by an injection tube which may be made of the same material as the sheath 3, for instance of a refractory material, and which is connected to a metal conductor 12.

The lower end of the injection tube 5 (FIG. 2), through which air is blown to renew the oxygen against the wall of the electrolyte, may be cut obliquely so that the tube 5 may be introduced into the liquid silver, whilst allowing the air current l5 to escape above the silver 11, thus avoiding bubbling, which would be produced if air would be allowed to escape after having passed through the silver. The current is thus led through the silver 11 and through the tube 5 for the injection of air, and that tube is preferably made of a refractory material, good conductor of current, for instance of stainless steel, and is connnected with the voltmetre (not shown) by a metal conductor 12.

Advantageously, in FIG. 1 as in FIG. 2 the tube 2 is made of zirconia (ZrO,) fully or partially stabilized by CaO, Y, O, or MgO.

when the sheath 3 is used for copper, it may be made of a current conductor cermet, for instance of Cr AI,O,, or of refractory steel, for instance ferritic steel containing chrome, or an alloy such as kanthal which contains iron and aluminum, in the case of lead, use will preferably be made of an iron sheath.

In FIG. 1 as in FIG. 2, the cement 4 forming the joint between the sheath 3 and the tube 2 may be made of an aluminous cement, such as a mixture of alumina with sodium silicate solution.

In FIG. 1 as in FIG. 2, a refractory ring 14 may advantageously be inserted between the sheath 3 and the tube 2, in order to help in fitting the tubes together and to reduce the thickness of the joint to be filled with cement 4. Alternatively, a refractory fibrous material may be used between the two tubes. A better fit and a better resistance to penetration by liquid metal of the space between the sheath 3 and the tube 2, are obtained.

in FIG. 3, the reference numeral shows the immersion apparatus, which is fixed to a wall 21 of a casting ladle 22 of launder through which the metal is flowing (not illustrated).

What I claim is:

1. Apparatus for the continuous measurement by immersion of oxygen contained in a molten metal which comprises:

a. a solid oxygen electrolyte tube having a closed bottom;

b. a reference electrode having known oxygen potential in contact with the inner surface of said tube;

c. the outer surface of said tube being adapted to be contacted with the molten metal which is to be tested;

d. means for measuring the electrochemical potential present between the reference electrode and the metal which is to be tested;

e. a refractory ring closely surrounding the sides of said electrolyte tube to provide resistance to penetration by the molten metal which is to be tested;

f. insulating means to protect said solid oxygen electrolyte tube against chemical attacks, thermal shocks and mechanical stress due to contact with the liquid molten metal;

g. said insulating means being an electrically conducting tube made of a metal containing substance selected from the group consisting of metal and cermet and having a high resistance to mechanical stress, to thermal shocks, to chemical attack, to splashing of the metal which is to be tested and to the slag of the metal which is to be tested;

h. said insulating means closely surrounding said refractory ring and being open at the bottom so that the outer surface of said electrolyte tube can be directly contacted with the molten metal which is to be tested;

i. said insulating means further being adapted to form a contact electrode with the molten metal; and

j. said refractory ring is joined to said solid oxygen electrolyte tube and to said insulating means by a refractory cement.

2. Apparatus as claimed in claim 1 characterized in that a block of metal material, which is of low melting point, is provided below the solid electrolyte, the block of metal being placed in contact with the bath and being capable of absorbing heat when it melts, to permit a progressive heating of the electrolyte.

3. Apparatus as claimed in claim 2 characterized in that a channel of small diameter is provided in the block of metal material, of low melting point, permitting the escape of gases present between the electrolyte tube and the block of metal material of low melting point.

4. The apparatus of claim 1 wherein said reference electrode consists of a metal and a constant flow of air which is continuously renewed in order to insure a constant percentage and wherein said reference electrode is located inside said solid electrolyte tube.

5. Apparatus of claim 1 wherein said metal containing substance is a refractory alloy.

6. Apparatus of claim 1 wherein said metal containing substance is ferritic steel containing chrome.

7. The apparatus of claim I which includes an injection means located inside the insulating means and inside the solid oxygen electrolyte tube and extending as near to the closed bottom of the electrolyte tube as possible in order to conduct air to the point of electrical contact with the closed bottom of said solid oxygen electrolyte tube; and wherein said injection means is made of a material which is refractory and which is a non-conductor.

8. The apparatus of claim 1 wherein said insulating means has a tongue which extends 4 to 5 centimeters beyond said solid oxygen electrolyte tube.

9. The apparatus of claim 1 wherein said solid oxygen electrolyte tube is a solid electrolyte tube of zirconia partially stabilized with a member selected from the group consisting of Y,O CaO, and MgO.

10. The apparatus of claim I wherein said insulating means is made of a material selected from the group of Cr M 0 ferritic steel containing chrome, kanthal alloy, and iron.

11. Apparatus for the continuous measurement by immersion of oxygen contained in a molten metal which comprises:

a. a solid oxygen electrolyte tube having a closed bottom;

b. a reference electrode having known oxygen potential in contact with the inner surface of said tube;

c. the outer surface of said tube being adapted to be contacted with the molten metal which is to be tested;

d. means for measuring the electrochemical potential present between the reference electrode and the metal which is to be tested;

. insulating means to protect said solid oxygen electrolyte tube against chemical attacks, thermal shocks and mechanical stress due to contact with the liquid molten metal;

. said insulating means being an electrically conducting tube made of a metal containing substance selected from the group consisting of metal and cermet and having a high resistance to mechanical stress, the thermal shocks, to chemical attacks, to splashing of the metal which is to be tested and to the slag of the metal which is to be tested;

g. said insulating means being open at the bottom so that the outer surface of said electrolyte tube can be directly contacted with the molten metal which is to be tested;

h. said insulating means further being adapted to form a contact electrode with the molten metal; and

i. said insulating means has a tongue which extends 4 to 5 centimeters beyond said oxygen electrolyte tube.

12. Apparatus as claimed in claim 11 characterized in that a block of metal material, which is of low melting point, is provided below the solid electrolyte, the block of metal being placed in contact with the bath and being capable of absorbing heat when it melts, to permit a progressive heating of the electrolyte.

13 Apparatus as claimed in claim 12 characterized in that a channel of small diameter is provided in the block of metal material, of low melting point, permitting the escape of gases present between the electrolyte tube and the block of metal material of low melting point.

14. The apparatus of claim 11 wherein said reference electrode consists of a metal and a constant flow of air which is continuously renewed in order to insure a constant percentage 0,; and wherein said reference electrode is located inside said solid electrolyte tube.

15. Apparatus of claim 11 wherein said metal containing substance is ferritic steel containing chrome.

16. Apparatus for the continuous measurement by immersion of oxygen contained in a molten metal which comprises:

a. a solid oxygen electrolyte tube having a closed bottom;

b. a reference electrode having known oxygen potential in contact with the inner surface of said tube;

c. the outer surface of said tube being adapted to be contacted with the molten metal which is to be tested; d. means for measuring the electrochemical potential said insulating means being an electrically conducting tube made of a metal containing substance selected from the group consisting of metal and cermet and having a high resistance to mechanical stress, to thermal shocks. to chemical attacks, to splashing of the metal which is to be tested and to the slag of the metal which is to be tested;

. said insulating means being open at the bottom so that the outer surface of said electrolyte tube can be directly contacted with the molten metal which is to be tested;

. said insulating means further being adapted to form a contact electrode with the molten metal; and

. a layer of silver provided in said solid electrolyte tube forming a contact between said reference electrode and said means for measuring.

* I t I! l 

2. Apparatus as claimed in claim 1 characterized in that a block of metal material, which is of low melting point, is provided below the solid electrolyte, the block of metal being placed in contact with the bath and being capable of absorbing heat when it melts, to permit a progressive heating of the electrolyte.
 3. Apparatus as claimed in claim 2 characterized in that a channel of small diameter is provided in the block of metal material, of low melting point, permitting the escape of gases present between the electrolyte tube and the block of metal material of low melting point.
 4. The apparatus of claim 1 wherein said reference electrode consists of a metal and a constant flow of air which is continuously renewed in order to insure a constant percentage O2; and wherein said reference electrode is located inside said solid electrolyte tube.
 5. Apparatus of claim 1 wherein said metal containing substance is a refractory alloy.
 6. Apparatus of claim 1 wherein said metal containing substance is ferritic steel containing chrome.
 7. The apparatus of claim 1 which includes an injection means located inside the insulating means and inside the solid oxygen electrolyte tube and extending as near to the closed bottom of the electrolyte tube as possible in order to conduct air to the point of electrical contact with the closed bottom of said solid oxygen electrolyte tube; and wherein said injection means is made of a material which is refractory and which is a non-conductor.
 8. The apparatus of claim 1 wherein said insulating means has a tongue which extends 4 to 5 centimeters beyond said solid oxygen electrolyte tube.
 9. The apparatus of claim 1 wherein said solid oxygen electrolyte tube is a solid electrolyte tube of zirconia partially stabilized with a member selected from the group consisting of Y2O3, CaO, and MgO.
 10. The apparatus of claim 1 wherein said insulating means is made of a material selected from the group of Cr + Al2O3, ferritic steel containing chrome, kanthal alloy, and iron.
 11. Apparatus for the continuous measurement by immersion of oxygen contained in a molten metal which comprises: a. a solid oxygen electrolyte tube having a closed bottom; b. a reference electrode having known oxygen potential in contact with the inner surface of said tube; c. the outer surface of said tube being adapted to be contacted with the molten metal which is to be tested; d. means for measuring the electrochemical potential present between the reference electrode and the metal which is to be tested; e. insulating means to protect said solid oxygen electrolyte tube against chemical attacks, thermal shocks and mechanical stress due to contact with the liquid molten metal; f. said insulating means being an electrically conducting tube made of a metal containing substance selected from the group consisting of metal and cermet and having a high resistance to mechanical stress, the thermal shocks, to chemical attacks, to splashing of the metal which is to be tested and to the slag of the metal which is to be tested; g. said insulating means being open at the bottom so that the outer surface of said electrolyte tube can be directly contacted with the molten metal which is to be tested; h. said insulating means further being adapted to form a contact electrode with the molten metal; and i. said insulating means has a tongue which extends 4 to 5 centimeters beyond said oxygen electrolyte tube.
 12. Apparatus as claimed in claim 11 characterized in that a block of metal material, which is of low melting point, is provided below the solid electrolyte, the block of metal being placed in contact with the bath and being capable of absorbing heat when it melts, to permit a progressive heating of the electrolyte.
 13. Apparatus as claimed in claim 12 characterized in that a channel of small diameter is provided in the block of metal material, of low melting point, permitting the escape of gases present between the electrolyte tube and the block of metal material of low melting point.
 14. The apparatus of claim 11 wherein said reference electrode consists of a metal and a constant flow of air which is continuously renewed in order to insure a constant percentage O2; and wherein said reference electrode is located inside said solid electrolyte tube.
 15. Apparatus of claim 11 wherein said metal containing substance is ferritic steel containing chrome.
 16. Apparatus for the continuous measurement by immersion of oxygen contained in a molten metal which comprises: a. a solid oxygen electrolyte tube having a closed bottom; b. a reference electrode having known oxygen potential in contact with the inner surface of said tube; c. the outer surface of said tube being adapted to be contacted with the molten metal which is to be tested; d. means for measuring the electrochemical potential present between the reference electrode and the metal which is to be tested; e. insulating means to protect said solid oxygen electrolyte tube against chemical attacks, thermal shocks and mechanical stress due to contact with the liquid molten metal; f. said insulating means being an electrically conducting tube made of a metal containing substance selected from the group consisting of metal and cermet and having a high resistance to mechanical stress, to thermal shocks, to chemical attacks, to splashing of the metal which is to be tested and to the slag of the metal which is to be tested; g. said insulating means being open at the bottom so that the outer surface of said electrolyte tube can be directly contacted with the molten metal which is to be tested; h. said insulating means further being adapted to form a contact electrode with the molten metal; and i. a layer of silver provided in said solid electrolyte tube forming a contact between said reference electrode and said means for measuring. 